Solvent refining hydrocarbon oil



Patented Dec. 27, 1938 UNITED STATES PATENT OFFIQE The Texas Company, poration of Delaware New York, N. Y., a cor- No Drawing. Application February 5, 1937, Serial No. 124,232

2 Claims.

This invention relates to solvent refining hydrocarbon oil, and oil derived from petroleum, particularly lubricating oil stocks.

Broadly, the invention contemplates-a method of separating hydrocarbon oil into fractions by extraction with a solvent in the presence of a material which facilitates efficient contact between the solvent and the oil undergoing treatment. The invention is particularly adapted to the solvent fractionation or refining of waxbearing mineral lubricating oil stocks with a low miscibility temperature type of selective solvent. Examples of such solvents are sulphur dioxide, dichlorethyl ether, phenol, nitrobenzene, etc.

These solvents are completely miscible with mineral lubricating oil at relatively low temperatures when mixed with the oil in substantial proportions.

More specifically, my invention contemplates extracting wax-bearing mineral lubricating oil with an extraction solvent of the above type in the presence of an added substance, such as a wax crystal modifying substance, which is adapted to modify the form of the crystal structure of the wax constituents present in the oil and thereby promote efiective contact between the solvent and the oil undergoing treatment. Suitable modifying substances may comprise glycerol, glycol stearate, aluminum stearate, or other metallic soaps, of higher fatty acids. Crude Montan wax, or the active ingredients thereof, may be used. Materials, such as Paraflow, which are known to be pour depressantsmay also be used.

An object of my invention is to adapt low miscibility temperature solvents of the type mentioned to the extraction of wax-bearing distillates and residua derived from. mineral oil. This type of wax-bearing stock usually contains relatively large amounts of wax and, as a result, may have a pour test of around 100 to 110 F., or evenhigher. Such oil does not lend itself particularly well to extraction or solvent fractionation at relatively low temperatures as, for example, up to about 150 F.

Therefore, the satisfactory employment of low miscibility temperature extraction solvents is largely precluded unless the oil is dewaxed prior to extraction. Usually, however, extraction of a dewaxed oil results in the production of a raflfinate oil having a somewhat higher pour test than that of the dewaxed oil. Consequently, it is generally desirable to extract prior to dewaxing.

Such solvents as exemplified by the examples given above, when mixed in equal proportion with wax-bearing oil, are completely miscible at temperatures around the pour point of the oil and lower.

In other words, separation of a mixture of oil with this type of solvent into phases is not realized at temperatures above that at which solid wax is present in the mixture. In order to effect phase separation, it is necessary to employ tem peratures at which wax constituents of the oil are present in solid form. The presence of the solidified wax interferes with the obtaining of efficient contact between the oil and the solvent for the reason that the wax crystals form a mass which occludes substantial amounts of the oil. The wax thus forms a barrier, preventing contact between the solvent and portions of the oil.

The process of my invention involves adding to the oil a small amount of wax crystal modifying substance, such as mentioned above, in order to inhibit or modify the formation of the wax crystals at the extraction temperature so that the solid wax is present in a condition which will permit the obtaining of more complete contact between oil and solvent. In the absence of this added inhibitor, the wax-bearing stock is in the form ofa mushy mass of oil and crystalline wax. However, when the inhibitor material is present during the extraction, the wax is present in a granular form which does not seriously interfere with the fluidity of the oil, and thus renders the; charge more susceptible to extraction with the solvent.

The presence of the modifier or wax crystal inhibitor also promotes more rapid settling so that the mixture of oil and solvent will more readily separate into extract and rafiinate phases. In some instances, the inhibitor material is of substantial benefit in preventing the formation of emulsions which are diflicult to break.

In carrying out the process of my invention, the pour depressant or modifying material is advantageously incorporated in the charge oil at elevated temperature prior to contact with the extraction solvent. For example, when employing Montan wax, or a mixture of Montan wax and aluminum stearate, as the modifying material, it is mixed with the charge oil in the proportion of about 0.10% to 1.0% by weight of the oil. Where Montan wax alone is used, it may be used in the proportion of about 0.15% to 0.25% by weight of the oil. This mixture may be heated to a temperature of around 160 or 180 F. in order to effect solution of the modifying substance in the oil. Higher temperatures, for example, 200 F. and above, may be employed to insure complete solution.

into contact with the extraction solvent in the proper proportion and under conditions of temperature suitable to effect the desiredseparation into extract and raflinate phases.

The extraction may be effected in a batch operation. On'the other hand, it may be carried out either in stage or continuous countercurrent' operation.

A preferred mode of extraction involves the employment of a countercurrent extraction tower provided with suitable packing material. In such a case, the wax-bearing oil containing the modifying substance 'is introduced to the lower portion of the tower, while thesolvent is introducedto the upper portion thereof. The ratio of solvent to oil would depend upon the nature of the oil undergoing treatment as well as the degree of extraction desired. Usually this will range from around one to four parts of solvent to'one part of oil.

In the case of these low miscibility tempera ture solvents, the extraction temperature, of course, may range from about 30 to or F. Under such conditions, an extract phase accumulates in the lower portion of the tower comprising low viscosity index or non-paraffinoid constituents of the oil dissolved in the bulk of the solvent liquid. The rafiinate phase accumulates in the upperportion of the tower and comprises the high viscosity index or paraf finoid constituents of the 'oil including wax mixed with a small amount of the solvent and containing the larger proportion of the modifying material.

These phases aresep-arately withdrawn and subjected to such furthertreatment as may be desired. In the case of the extract'phase, this may involve merely stripping torecover the solvent. In the case of the rafiinate phase, since it' contains the wax constituents of the oil, it will be desirable to subject the mixture to dewaxing, in which case it is mixed with an additional quantity of the selective solvent as well as a quantity of a suitable modifying solvent, such as benzol, in order to provide a solvent mixture which will have selective action as between wax and oil at temperatures of 0 F. and below.

The wax crystal modifying material'retained' in the raffinate phase is of advantage in the dewaxing stepin aiding the separation of the wax.

Thereafter, the resulting mixtureis brought,

Where the modifying material is crude Montan wax, aluminum stearate, or a mixture thereof, for example, it exerts substantial benefit and causes precipitation of the solid hydrocarbons during chilling in the form of Wax crystals which can be rapidly removed by filtration.

Whileextraction with a single selective solvent has been described above, it is also contemplated that the extraction solvent may be employed in conjunction'with auxiliary solvents,

uents, at a temperature of around 100 to- 150 F., the character of the oil and solvent being such that appreciable emulsification occurs during extraction, the method of inhibiting emulsification during said extraction and separation into phases comprising incorporating in the oil a small amount of material comprising a metallic soap of a higher fatty acid and effecting phase separation in the presence of said material at the aforesaid temperature.

2. In the extraction of lubricating oil with a selective solvent to separate the oil into an extract phase rich in naphthenicconstituents, and

a .rafiinate phase rich in paraifinic constituents at temperatures substantially above the dewaxing temperature of the oil, the character of the oil and solvent being such that appreciable emulsification occurs during extraction and separation into phases, the method of inhibiting emulsification during said extraction and separation into phases comprising incorporating in the oil a small amount ofmaterial comprising a metallic soap of a higher fatty acid and effecting separation'into phases in the presence of said mate rial at a temperature substantially above the dewaxing temperature.

LE ROY G. STORY. 

